Over the last few years it has become increasingly common to connect personal computers or workstations together into networks so that different machines can communicate with one another. A typical approach has been the introduction of local area networks (LANs) that provide file transfer and other facilities between computers.
There is a continuing need to achieve more natural and effective communications between users--for example, to enable collaborative working, in which users of two or more different machines work simultaneously and in combination on a single application (for example a spreadsheet). This application will be running on just one of the machines, but its output will be displayed at the other workstations, so that multiple users can interact with the application.
A central aspect of collaborative working and other similar environments is the need for any modifications to the application display (for example a change in a graph) to appear as near simultaneously on all screens as possible. Too large a delay in displaying such modifications on remote terminals removes the spontaneity of collaborative working, and so loses most of the benefits. A major problem in achieving this simultaneity between workstations is that the connections between the computers have a limited bandwidth. This is particularly so if telephone-based ISDN lines or similar are used. One way of coping with this is to use data compression, to reduce the amount of data that must be transmitted. However, data compression is expensive in processing time, so that although time is saved in transmission, a delay is introduced by the compression itself.
Accordingly, the invention provides a computer workstation adapted for connection into a network of one or more other computers, the computer workstation including a screen, means for sending requests to the screen to update the contents of portions thereof, and means for transmitting the contents of the screen to other computers in the network, and characterized by means, responsive to said requests, for identifying the portion of the screen to be updated by a request, and means for selecting the contents of the portion of the screen updated by the request to be transmitted to another computer.